Examples of disclosed literature related to lithium-ion secondary batteries include Patent Literature 1 to 5 below.
Patent Literature 1 discloses an invention related to a non-aqueous electrolyte solution secondary battery. The non-aqueous electrolyte solution secondary battery disclosed in Patent Literature 1 is structured such that a positive electrode forming a positive electrode mixture layer and a negative electrode are immersed in a non-aqueous electrolyte solution. The positive electrode mixture layer contains a lithium transition metal complex oxide, an electrically conductive material mainly formed of a graphite carbon material, and a binder. The positive electrode mixture layer is approximately uniformly applied to a positive electrode current collector. In addition, a lithium transition metal complex oxide with a layered crystalline structure and an average particle diameter of 5 to 20 μm is used as the lithium transition metal complex oxide. Patent Literature 1 discloses that a proportion of a volume of holes in the positive electrode mixture layer among a volume of the positive electrode mixture layer is 25% or higher and 35% or lower. Patent Literature 1 also discloses that, due to the structure described above, an amount of the non-aqueous electrolyte solution in the positive electrode mixture layer is optimized, a distribution of the non-aqueous electrolyte solution becomes approximately uniform, and diffusivity of lithium ions and electron conductivity are secured.
In addition, a non-aqueous electrolyte solution secondary battery disclosed in Patent Literature 2 is structured such that a positive electrode layer including a lithium complex metal oxide containing nickel and a vinylidene fluoride-based fluoro-rubber is supported by a current collector. Patent Literature 2 discloses that, as measured by a mercury intrusion method, the positive electrode layer has a porosity of 20% to 50% and a pore volume of 10 mm3/g to 150 mm3/g with respect to pores in a diameter range of 0.1 μm to 3 μm.
Furthermore, a non-aqueous electrolyte secondary battery disclosed in Patent Literature 3 comprises a positive electrode bearing an active material made of a spinel lithium manganese complex oxide. Furthermore, a BET specific surface area of the positive electrode active material is 1.5 m2/g or less, an average particle diameter of primary particles ranges from 0.5 μm to 5 μm, an average particle diameter of secondary particles ranges from μm to 30 μm, and a porosity of the positive electrode ranges from 15% to 40%.
Moreover, Patent Literature 4 discloses a gel electrolyte battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte solution containing an electrolyte salt, and a gel electrolyte made of matrix macromolecules. The gel electrolyte battery disclosed in Patent Literature 4 comprises a positive electrode mixture layer containing a positive electrode active material. In addition, a porosity of the positive electrode mixture layer with respect to hole diameters of 0.6 μm or more is within a range of 18% or higher and 34% or lower.
In addition, Patent Literature 5 discloses a positive electrode active material of a lithium secondary battery having a crystalline structure made of a spinel manganese complex oxide. In this case, the manganese complex oxide is expressed by the chemical formula Li1-xMn1-x-yMyO4 (where 0≦x≦0.4, 0≦y≦0.15, and M in the formula denotes at least one or more types of metal selected from a group consisting of Ni, Co, Cr, and Al). The positive electrode active material disclosed in Patent Literature 5 has holes formed inside particles. In addition, an amount of the holes inside the particles is set so that a ratio of a cross-sectional area of the holes inside a particle to a cross-sectional area of the particle ranges from 3.0% to 20%.